Providing content to a user across multiple devices

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on a computer-readable storage medium, and including a method for providing content. The method comprises receiving a first login associated with a first anonymous identifier and first device, creating an associated first private-public key pair, storing a first private key locally in the first device, and publishing a first public key. The method further comprises receiving a second login from a second different device, creating a second private-public key pair, storing a second private key, publishing the second public key, creating a secret key using the first public key, and associating a second anonymous identifier with the secret key. The method further comprises subsequently receiving a login the first device, creating the secret key using the second public key, associating the first anonymous identifier with the secret key, receiving a request for content from either device, and providing content using the association.

BACKGROUND

This specification relates to information presentation.

The Internet provides access to a wide variety of resources. For example, video and/or audio files, as well as web pages for particular subjects or particular news articles, are accessible over the Internet. Access to these resources presents opportunities for other content (e.g., advertisements) to be provided with the resources. For example, a web page can include slots in which content can be presented. These slots can be defined in the web page or defined for presentation with a web page, for example, along with search results.

Content item slots can be allocated to content sponsors as part of a reservation system, or in an auction. For example, content sponsors can provide bids specifying amounts that the sponsors are respectively willing to pay for presentation of their content. In turn, an auction can be run, and the slots can be allocated to sponsors according, among other things, to their bids and/or the relevance of the sponsored content to content presented on a page hosting the slot or a request that is received for the sponsored content. The content can then be provided to the user on any devices associated with the user such as a personal computer (PC), a smartphone, a laptop computer, or some other user device.

SUMMARY

In general, one innovative aspect of the subject matter described in this specification can be implemented in methods that include a computer-implemented method for providing creatives. The method comprises receiving a first login request from a first device used by a user for logging into a service, the first login request being associated with a first anonymous identifier associated with the first device. The method further comprises reading a seed and creating, using one or more processors, a first private-public key pair associated with the user when using the first device. The method further comprises storing a first private key associated with the first private-public key pair locally in the first device and publishing a first public key in a directory entry associated with the user. The method further comprises receiving a second login request from a second different device used by the user, the second login request being associated with a second different anonymous identifier associated with the second different device. The method further comprises, responsive to the received second login request: reading the seed and creating a second private-public key pair associated with the user when using the second different device including a second different public key, storing a second private key associated with the second private-public key pair locally in the second different device and publishing the second public key in the directory entry associated with the user, creating a secret key using the first public key, and associating the second anonymous identifier with the secret key. The method further comprises, at a time subsequent to the publishing of the second public key, receiving a login request from the user when accessing the first device and, responsive to the received request, creating the secret key using the second public key and associating the first anonymous identifier with the secret key. The method further comprises receiving a request for content from either the first device including the first anonymous identifier or the second different device including the second different anonymous identifier. The method further comprises providing, using the one or more processors, content in response to the request using the association.

These and other implementations can each optionally include one or more of the following features. The directory entry can be stored in a directory that includes one or more entries, each entry indexed by an identifier associated with a given user. The identifier can be a user login identifier. The identifier can be an email address associated with the user. The first and second different anonymous identifiers can be associated with different browsers. Receiving the login request can include receiving a request to log into a social service. The method can further comprise storing an association between the secret key and the first and second anonymous identifiers including storing the secret key, the first anonymous identifier, and the second different anonymous identifier as an entry in a table. Storing the association can include mapping the secret key to both the first and the second different anonymous identifiers. Storing the association can include removing the association after expiration of a first time period. The first time period can be associated with an amount of time after which the user would have been expected to have logged out from either the first device or the second different device. The first and second different anonymous identifiers can be selected from the group comprising a browser cookie or a device identifier. The method can further comprise receiving a login request from a third different device used by the user, the login request being associated with a third different anonymous identifier associated with the third different device; creating a third different public-private key pair including a third public key; storing the third private key locally on the third different device and publishing the third public key; creating the secret key using one of either the first public key or the second public key; storing an association between the secret key, the first anonymous identifier, the second different anonymous identifier and the third different anonymous identifier; receiving a request for content from either the first device including the first anonymous identifier, the second different device including the second different anonymous identifier, or the third different device including the third different anonymous identifier; and providing content in response to the request and using the association. Receiving a request for content can include receiving a request for advertising content. Receiving a request for content can include receiving a request from the first device including the first anonymous identifier, where the first anonymous identifier is a cookie. Providing content in response to the request can further include identifying the user based on the association and providing content of interest to the user.

In general, another innovative aspect of the subject matter described in this specification can be implemented in methods that include another computer-implemented method for providing creatives. The method comprises linking, using one or more processors, multiple anonymous identifiers associated with a user by a service using a key exchange protocol without storing personally identifiable information associated with the user in the linking. The method further comprises receiving, at the service, requests for content from a client device associated with the user, where each request includes one of the anonymous identifiers. The method further comprises providing, using the one or more processors, content associated with the user, responsive to the received requests and based on the linking.

These and other implementations can each optionally include one or more of the following features. Linking multiple anonymous identifiers can include: receiving a login request from the user from plural different devices; determining a secret key using published public key information from another device associated with the user, where the secret key does not include any personally identifiable information associated with the user; and mapping the secret key to an anonymous identifier associated with each login request. The multiple anonymous identifiers can be selected from the group comprising browser cookies and device identifiers. Determining the secret key include, at each device: creating a public-private key pair; publishing a public key of the public-private key pair; and using a private key of the public-private key pair and a public key of another device to compute the secret key.

In general, another innovative aspect of the subject matter described in this specification can be implemented in methods that include another computer-implemented method for providing creatives. The method comprises creating, using one or more processors, public-private key pairs for a user each time the user logs into a service from a different device including publishing respective public keys of the user in a directory entry associated with the user. The method further comprises creating, by each device, a secret key using a public key of another device that is stored in the directory that does not include personally identifiable information associated with users. The method further comprises associating the secret keys with a plurality of anonymous identifiers, each anonymous identifier assigned to the user when logged into a respective different device. The method further comprises providing, using the one or more processors, content associated with the user and based at least in part on the association.

Particular implementations may realize none, one or more of the following advantages. Content can be provided to a user based at least in part on prior delivered content, such as content previously delivered to a user on one of a plurality of different devices. Associations among anonymous identifiers can be used enable delivery of interesting content to a user. Content sponsors can be provided with more precise mechanisms for delivering content to users.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example environment for delivering content.

FIGS. 2A through 2E collectively show an example system for providing content to a user who is recognized when using multiple different devices.

FIG. 2F shows example calculations of public, private and secret keys.

FIG. 3A is a flowchart of an example process for providing content to a user on any of multiple devices associated with the user.

FIG. 3B is a flowchart of an example process for providing content to a user on any of multiple devices associated with the user.

FIG. 3C is a flowchart of an example process for providing content to a user on any of multiple devices using public-private keys.

FIG. 4 is a block diagram of an example computer system that can be used to implement the methods, systems and processes described in this disclosure.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

This document describes methods, processes and systems for providing content to a user having or being associated with multiple devices, without storing personally identifiable information associated with the user to facilitate content selection. For example, when a user logs onto a user service from a first device (e.g., the user's home PC), a public key-private key pair can be determined and the public key can be published. The public key can be associated with the user's first device and stored by the user service. The private key can be stored locally. Subsequently, when the user logs into the service from a second different device, the second different device can also determine a public-private key pair. Each device can subsequently compute a secret key using the device's own private key and the other device's published public key. The secret key can be stored in combination with anonymous identifiers of each device, thus creating a linking or association between the devices.

In some implementations, the anonymous identifiers can be cookies, browser cookies, device identifiers, or other identifiers that are associated with each device. As a result, the mapping can identify all of the devices associated with the user without storing personally identifiable information (PII) associated with the user. When content is subsequently provided to the user on any of the devices, information included in the mapping can be used to assist in selecting relevant content to be provided to the user. The selection of relevant content can include decisions regarding how content is delivered to the user, such as and including, limitations on when or how content is delivered. For example, the number of impressions of an advertisement can be limited to a fixed number of impressions per user per time period regardless of how many devices the user uses.

In some implementations, anonymous identifiers can be associated with different browsers or other applications on the same device. For example, the techniques described in this disclosure can be used to link two or more identifiers of applications that may have different cookie spaces on the same device, or applications on different devices, or a combination of both.

In some implementations, linking anonymous identifiers can be used in handshaking among mobile applications or a combination of mobile applications, browsers and other applications. For example, mobile applications may each have their own cookie space even on the same device which can prevent handshaking with other applications. Each mobile application can use the techniques described herein to generate, for example, a private key an a public key, publish the public key, access public keys of other mobile applications (or associated with other devices), and compute secret keys using their own private keys and the public keys of other mobile applications (or associated with other devices).

In some implementations, users may be provided with an opportunity to opt in/out of programs or features that allow the user to be discovered across multiple devices and/or to be provided content based on the discovery.

In some implementations, the mapping process can be repeated periodically to ensure that the anonymous identifiers (e.g., cookies) are not stale, thus keeping session history information for the user up-to-date. For example, cookies on a computer can expire over time, or a user can clear a cookie, resulting in setting a new cookie. Repeating the cookie-mapping process periodically can ensure that the current set of cookies belonging to the user are correctly mapped. While reference is made to cookies, other forms of anonymous identifiers that include or have been derived from a seed can be used.

In some implementations, user session history information can be stored anonymously. For example, the session history information can include a user's browsing history, the times that the user has seen a particular advertisement, and other session history information. The information can be stored in association with the anonymous identifiers described herein. In some implementations, session history information associated with the user's session on a first device can be stored in a table that includes the anonymous identifier associated with the first device. The same table can also be used to store the same user's session history information for the user's session on a second device. In some implementations, a separate or the same table can be used to store associations among the anonymous identifiers. In some implementations, anonymous identifiers, the associations (e.g., linking to the secret key), and the session data all can be stored, for example, without any corresponding personally identifiable information for a given user.

As will be described in further detail below, subsequent to the storage of the association and session history information, a request for content (e.g., an advertisement) can be sent from any of the devices associated with that user (the request including an anonymous identifier associated with a given device). In some implementations, the session history information stored in the tables can be used in determining, for example, advertisements that may be of interest to the user responsive to the received request. The determination can include inferences for the user based on the user's stored session history information. In some implementations, the session history information for the user can be aggregated, e.g., by joining tables using the anonymous identifiers. For example, a request for content can be received, and the request can include an anonymous identifier associated with a user's desktop device. The received anonymous identifier can be used to look up the user's other anonymous identifiers (e.g., for mobile and other devices of the user). The retrieved set of anonymous identifiers can be used access to session history information in the other tables (e.g., user browsing history). In some implementations, all of the session history information can be joined together for the respective devices producing aggregated information. In some implementations, the aggregated session history information can be provided to a content management system in order to determine and select eligible content for delivery to the user responsive to the received request. For example, because the session history information can include the number of times that the user has seen a particular advertisement, the content management system can help to avoid selecting an advertisement for the user which has already been presented a predetermined number of times.

In some implementations, aggregating the information can occur on demand, e.g., in real time after a request for content occurs. For example, the user's session history information, stored individually by anonymous identifier in the various tables, can be joined. Aggregating the information in real time can solve issues, for example, related to whether the user has opted out of being provided content based on the devices used by the user. For example, session history information for a device for which the user has opted out will not be aggregated with other session history information. In some implementations, the information for a user can be aggregated and stored in advance of any requests for content. For example, all of the user session history information can be stored in a third table, e.g., that includes all of the user session history information across all of the user's devices.

FIG. 1 is a block diagram of an example environment 100 for delivering content. The example environment 100 includes a content management system 110 for selecting and providing content in response to requests for content. The example environment 100 includes a network 102, such as a local area network (LAN), a wide area network (WAN), the Internet, or a combination thereof. The network 102 connects websites 104, user devices 106, content sponsors 108 (e.g., advertisers), publishers 109, and the content management system 110. The example environment 100 may include many thousands of websites 104, user devices 106, content sponsors 108 and publishers 109.

In some implementations, the example environment 100 further includes a user login service 120 that can provide, for any particular user, access to the user's Web services, e-mail, social networks, business applications or other resources. For example, the user login service 120 can receive login requests from the user, such as through a Web browser or other application running on any device associated with the user. The login request can include, for example, the user's login ID (e.g., a unique identifier, an email address, a phone number, or any other identifier for the user that can be used for verifying the user at login). The user login service 120 can also maintain information related to the devices on which the user is currently logged on, or has been logged into recently. The information can include, for example, a mapping of anonymous identifiers for the devices with a session key that does not contain personally identifiable information associated with the user. In some implementations, the mapping can be stored, for each user, in a data store of linked anonymous identifiers 122, or in some data structure.

In some implementations, the user login information 121 or some other data store can store user login IDs, public keys and initial seeds. For example, the information can be used by a second device used by a user to access the public key published by a first device used by the same user. Similarly, the user's first device can access the public key published by the second device. At the same time, seed values can be read from the user login information 121 by any of the user's devices and used to determine a secret key.

A data store of user opt-out and privacy preferences 142 can include information that the user has provided regarding if and how information about the user's different devices can be used. For example, users can use one or more user preferences web page that may be part of (or separate from) the user login service 120. In some implementations, users can set a preference that says, “Do not link my different devices,” or selectively identify which devices are allowed (or not allowed) to be linked. Then, before any operation is performed that may link the anonymous identifiers of the user's different devices, the user's user opt-out and privacy preferences 142 can be checked, and the linking will be performed only if allowed by the user. In some implementations, the user may specify settings that prohibit providing content based on the linking. For example, while the user may allow his smart phone and PC to be linked, the user may decide that no content (e.g., advertisements) should be provided based on the linking.

A website 104 includes one or more resources 105 associated with a domain name and hosted by one or more servers. An example website is a collection of web pages formatted in hypertext markup language (HTML) that can contain text, images, multimedia content, and programming elements, such as scripts. Each website 104 can be maintained by a content publisher, which is an entity that controls, manages and/or owns the website 104.

A resource 105 can be any data that can be provided over the network 102. A resource 105 can be identified by a resource address that is associated with the resource 105. Resources include HTML pages, word processing documents, portable document format (PDF) documents, images, video, and news feed sources, to name only a few. The resources can include content, such as words, phrases, images, video and sounds, that may include embedded information (such as meta-information hyperlinks) and/or embedded instructions (such as JavaScript scripts).

A user device 106 is an electronic device that is under control of a user and is capable of requesting and receiving resources over the network 102. Example user devices 106 include personal computers (PCs), televisions with one or more processors embedded therein or coupled thereto, set-top boxes, mobile communication devices (e.g., smartphones), tablet computers and other devices that can send and receive data over the network 102. A user device 106 typically includes one or more user applications, such as a web browser, to facilitate the sending and receiving of data over the network 102.

A user device 106 can request resources 105 from a website 104. In turn, data representing the resource 105 can be provided to the user device 106 for presentation by the user device 106. The data representing the resource 105 can also include data specifying a portion of the resource or a portion of a user display, such as a presentation location of a pop-up window or a slot of a third-party content site or web page, in which content can be presented. These specified portions of the resource or user display are referred to as slots (e.g., ad slots).

To facilitate searching of these resources, the environment 100 can include a search system 112 that identifies the resources by crawling and indexing the resources provided by the content publishers on the websites 104. Data about the resources can be indexed based on the resource to which the data corresponds. The indexed and, optionally, cached copies of the resources can be stored in an indexed cache 114.

User devices 106 can submit search queries 116 to the search system 112 over the network 102. In response, the search system 112 accesses the indexed cache 114 to identify resources that are relevant to the search query 116. The search system 112 identifies the resources in the form of search results 118 and returns the search results 118 to the user devices 106 in search results pages. A search result 118 can be data generated by the search system 112 that identifies a resource that is responsive to a particular search query, and includes a link to the resource. In some implementations, the search results 118 include the content itself, such as a map, or an answer, such as in response to a query for a store's products, phone number, address or hours of operation. In some implementations, the content management system 110 can generate search results 118 using information (e.g., identified resources) received from the search system 112. An example search result 118 can include a web page title, a snippet of text or a portion of an image extracted from the web page, and the URL of the web page. Search results pages can also include one or more slots in which other content items (e.g., ads) can be presented. In some implementations, slots on search results pages or other web pages can include content slots for content items that have been provided as part of a reservation process. In a reservation process, a publisher and a content item sponsor enter into an agreement where the publisher agrees to publish a given content item (or campaign) in accordance with a schedule (e.g., provide 1000 impressions by date X) or other publication criteria. In some implementations, content items that are selected to fill the requests for content slots can be selected based, at least in part, on priorities associated with a reservation process (e.g., based on urgency to fulfill a reservation).

When a resource 105, search results 118 and/or other content are requested by a user device 106, the content management system 110 receives a request for content. The request for content can include characteristics of the slots that are defined for the requested resource or search results page, and can be provided to the content management system 110.

For example, a reference (e.g., URL) to the resource for which the slot is defined, a size of the slot, and/or media types that are available for presentation in the slot can be provided to the content management system 110. Similarly, keywords associated with a requested resource (“resource keywords”) or a search query 116 for which search results are requested can also be provided to the content management system 110 to facilitate identification of content that is relevant to the resource or search query 116.

Based at least in part on data included in the request, the content management system 110 can select content that is eligible to be provided in response to the request (“eligible content items”). For example, eligible content items can include eligible ads having characteristics matching the characteristics of ad slots and that are identified as relevant to specified resource keywords or search queries 116. In some implementations, the selection of the eligible content items can further depend on user signals, such as demographic signals and behavioral signals. Other information, such as user identifier information that is associated with the mappings described above, can be used and/or evaluated when selecting eligible content.

The content management system 110 can select from the eligible content items that are to be provided for presentation in slots of a resource or search results page based at least in part on results of an auction (or by some other selection process). For example, for the eligible content items, the content management system 110 can receive offers from content sponsors 108 and allocate the slots, based at least in part on the received offers (e.g., based on the highest bidders at the conclusion of the auction or based on other criteria, such as those related to satisfying open reservations). The offers represent the amounts that the content sponsors are willing to pay for presentation (or selection) of their content with a resource or search results page. For example, an offer can specify an amount that a content sponsor is willing to pay for each 1000 impressions (i.e., presentations) of the content item, referred to as a CPM bid. Alternatively, the offer can specify an amount that the content sponsor is willing to pay (e.g., a cost per engagement) for a selection (i.e., a click-through) of the content item or a conversion following selection of the content item. For example, the selected content item can be determined based on the offers alone, or based on the offers of each content sponsor being multiplied by one or more factors, such as quality scores derived from content performance, landing page scores, and/or other factors.

A conversion can be said to occur when a user performs a particular transaction or action related to a content item provided with a resource or search results page. What constitutes a conversion may vary from case-to-case and can be determined in a variety of ways. For example, a conversion may occur when a user clicks on a content item (e.g., an ad), is referred to a web page, and consummates a purchase there before leaving that web page. A conversion can also be defined by a content provider to be any measurable or observable user action, such as downloading a white paper, navigating to at least a given depth of a website, viewing at least a certain number of web pages, spending at least a predetermined amount of time on a web site or web page, registering on a website, experiencing media, or performing a social action regarding a content item (e.g., an ad), such as republishing or sharing the content item. Other actions that constitute a conversion can also be used.

In some implementations, the likelihood that a conversion will occur can be improved, such as by recognizing a user when the user has accessed resources using multiple devices. For example, if it is known that a content item (e.g., an advertisement) has already been seen by a user on a first device (e.g., the user's home PC), then a determination can be made (e.g., through parameters) whether or not to provide the same content item to the same user on a different device (e.g., the user's smartphone). This can increase the likelihood of a conversion, for example, by either repeating impressions of an advertisement or avoiding subsequent impressions, depending on how multiple impressions for the advertisement to the same user are predicted to lead to a conversion in either case.

For situations in which the systems discussed here collect personal information about users, the users may be provided with an opportunity to opt in/out of programs or features that may collect personal information (e.g., information about a user's social network, social actions or activities, a user's preferences or a user's current location). In addition, certain data may be anonymized in one or more ways before it is stored or used, so that personally identifiable information associated with the user is removed. For example, a user's identity may be anonymized so that the no personally identifiable information can be determined for the user, or a user's geographic location may be generalized where location information is obtained (such as to a city, ZIP code, or state level), so that a particular location of a user cannot be determined.

FIGS. 2A-2E collectively show an example system 200 for providing content to a user who is recognized when using multiple different devices. In some implementations, recognition of the user across different devices can be achieved by linking anonymous identifiers of the user's multiple different devices. As an example, an anonymous identifier 206 a of a first device 106 a (e.g., a desktop computer of a user 202) can be linked to an anonymous identifier 206 b of a second different device 106 b (e.g., a laptop computer of the user 202). In some implementations, the system 200 can be part of the environment 100 that is described above with reference to FIG. 1. An example sequence of events (e.g., with numbered steps 0 and 1a through 8) follows for associating the anonymous identifiers 206 a and 206 b and providing content based on the association. However, other sequences can also be used to link devices 106 a, 106 b and additional devices 106 associated with the user 202. In some implementations, the devices 106 a, 106 b and additional devices 106 can be linked using associations stored in the linked anonymous identifiers 122. The associations can be stored, for example, without storing any personally identifiable information for the user 202.

Before any linking occurs using the anonymous identifiers associated with a user's different devices, the user login service 120 (or the content management system 110) can check 107 the user's user opt-out and privacy preferences 142 to see if the user has opted out of such linking. For example, if the user has specified not to allow the user's devices to be linked (or use information thereof), then steps 2a though 6b will not occur, and the content provided in step 8 may be different.

In some implementations, a first step 1a (e.g., as allowed by the user) of the sequence of steps can occur, for example, when the user 202 logs into the first device 106 a (e.g., the user's desktop computer) using a login service (not shown in FIGS. 2A-2D). For example, the login service or some other component can receive a login request 208 a from the first device 106 a. The login request 208 a can be associated with the anonymous identifier 206 a (e.g., a cookie or device identifier) associated with the first device 106 a. In some implementations, the login request 208 a and/or other login requests can be requests to log into a social service.

In some implementations, the user login information 121 can store user login IDs 210, initial seed numbers 212 and public keys 214 associated with multiple users. The user login information 121, for example, can serve as a directory that includes one or more entries, each entry indexed by an identifier associated with a given user (e.g., user login identifier, email address, or some other identifier). For example, when the user 202 logs into the device 106 a using the login service, information stored for the user in the user login information 121 can include a login ID 210 a, a seed 212 a (e.g., a generator-prime pair, such as 7, 11, that is usable by all of the user's devices), and, as will be discussed in further detail below, a public key 214. At the current stage of the sequence of steps, the public key 214 has not yet been determined for the current user. In some implementations, seeds 212 can vary by user, e.g., the seed 212 b (e.g., generator-prime pair 7, 13) for a second user can be different from the seed 212 a.

At step 2a, the first device 106 a can read a seed 216 a (e.g., a generator-prime pair 7, 11 from the user login information 121) and create a private-public key pair that is associated with the user 202 using the first device 106 a. In some implementations, creating the private-public key pair can include, at step 3a, computing 218 a a private key (e.g., 9) and computing a public key (e.g., 4). In some implementations, generation of public and private keys can use generator G, prime P pair (e.g., 7, 11), where G<P, an example of which is described with reference to FIG. 2F. At step 4a, the public key is published 220 a, e.g., stored as the public key 214 a. The private key n and the public key 4 constitute the private-public key pair, yet each typically is stored in a different location. For example, the private key n can be stored locally on the first device 106 a, .e.g., in local storage 219. The public key (e.g., 4) can be stored in the user login information 121 as the public key 214 a. In some implementations, the public key 214 a can be stored in a row 222 that includes user login information for the user 202 on one or more devices (e.g., devices 106 a and 106 b in the current example). For example, the row 222 can serve as a directory entry associated with the user 202. Each of the other rows can be used to store information for a different user.

Referring now to FIG. 2B, at step 2b, after a login by the user on a second different device 106 b, a seed 216 b (e.g., the generator-prime pair 7, 11) can be read (e.g., from the user login information 121) and a second private-public key pair that is associated with the user can be created. The second private-public key pair is associated with the user 202 using the second device 106 b. For example, the second private-public key pair is different than the private-public key pair that is associated with the login by the user 202 on the first device 106 a. In some implementations, creating the second private-public key pair can include, at step 3b, computing 218 b a private key (e.g., m) and computing a second public key (e.g., 8). At step 4b, the second public key is published 220 b, e.g., by adding the second public key to the set of public keys stored as the public keys 214 a. The private key m and the public key 8 constitute the second private-public key pair (e.g., <m, 8>), the values of which are different from those of the private-public key pair computed for the first device 106 a (e.g., <n, 4>). In some implementations, the private key m can be stored locally on the second different device 106 b, e.g., in local storage 221 b. The public key (e.g., 8) can be stored, for example, in user login information 121 with the public key 4 from the first device 106 a. As a result, the directory entry stored in the row 222 (and associated with the user 202) is updated, now including two public keys.

Referring now to FIG. 2C, at step 5a, the second different device 106 b can create a secret key 226 a (e.g., 3) using the public key (e.g., 4) from the first device 106 a and the second private key (e.g., private key m from local storage 221 b). At step 6a, the second different device 106 b can also associate 228 a the second anonymous identifier (e.g., “Device ID 2”) with the secret key (e.g., 3). In some implementations, the association can include storing the association, e.g., in the linked anonymous identifiers 122. For example, the linked anonymous identifiers 122 can include secret keys 230 and anonymous identifiers of the same users 232. For example, a row 234 can include a secret key 230 a (e.g., 3 or a hashed representation of 3) and the anonymous identifier 232 b (e.g., “Device ID 2”) that corresponds to the association that occurred in step 6a. At a time subsequent to the publishing of the second public key (e.g., 8), and after the secret key 3 has been computed and an association stored (e.g., as a hashed representation) with the second different device 106 b, the user may log in again at the first device 106 a. As a result, a login request 208 c can be received (e.g., by the login service) from the user at the first device 106 a. For example, the login request 208 c can be similar to the login request 208 a described above. However, in this case, the login service, for example, can determine that a public key exists for another device associated with the user, e.g., the second different device 106. Using the additional public key, a link or association can be made between the two devices 106 a and 106 b as described in further detail below. In some implementations, whenever the secret key is stored, the stored value can be a hashed version of the secret key, e.g., using a one-way hash function.

Referring now to FIG. 2D, at step 5b, in response to the login request 208 c, the first device 106 a can create a secret key 226 b (e.g., 3) using the public key (e.g., 8) from the second different device 106 b and the first private key (e.g., private key n from local storage 221 a). For example, the secret key can match the secret key computed by the second different device 106 b. At step 6b, the first device 106 a can also associate 228 b the second anonymous identifier (e.g., Device ID 2) with the secret key (e.g., 3). In some implementations, the association can include storing the association, e.g., in the linked anonymous identifiers 122. For example, the row 234 containing the secret key 230 a (e.g., 3) and the anonymous identifier 232 b (e.g., “Device ID 2”) can be updated to also include the anonymous identifier 232 a (e.g., “Device ID 1”). As a result of storing the association, the anonymous identifiers 206 a and 206 b, as well as the devices 106 a and 106 b, are now linked. Further, the association among the user's various devices is achieved without storing any personally identifiable information associated with the user.

In some implementations, it is possible that one or more anonymous identifiers such as anonymous identifier 232 a or anonymous identifier 232 b can appear in multiple rows (e.g., three or more) in the linked anonymous identifiers 122. This can be an indication, for example, that the device associated with the anonymous identifier is a shared device (e.g., at a library or an Internet café). In this example, the logins by several different users (e.g., three or more) would result in the creation of multiple rows in the anonymous identifiers 122, each having the same anonymous identifier. In some implementations, when highly-shared devices are detected in this way, the highly-shared devices can be un-linked, or other considerations can be taken. For example, thresholds can be established, and if a cookie or other anonymous identifier appears in more than three rows, the associated can be considered a shared machine.

Referring to FIG. 2E, at step 7, the content management system 110 can receive a request for content 240 a or 240 b (e.g., a request for advertising content) from either the first device 106 a or the second different device 106 b. For example, the request for content 240 a can be a request for an advertisement to fill an advertisement slot 242 a on a web page 244 a displayed on the first device 106 a. In another example, the request for content 240 b can be a request for an advertisement to fill an advertisement slot 242 b on a web page 244 b displayed on the second different device 106 b. If the request for content 240 a is from the first device 106 a, for example, then the request for content can include the first anonymous identifier 232 a. Otherwise, if the request for content 240 b is from the second different device 106 b, for example, then the request for content can include the second different anonymous identifier 232 b.

Regardless of where the request for content originates, at step 8, the content management system 110 can provide a content item (e.g., content items 246 a or 246 b) in response to the request and using the association that maps the user 202 to multiple devices (e.g., from the linked anonymous identifiers 122). For example, the association can be represented by information in the row 234 that associates anonymous identifiers 232 a and 232 b, e.g., based on the same secret key 230 a. Using this information, the content management system 110 can, for example, treat the requests for content as if they originate from the same user, regardless of the particular user device. In some implementations, identifying eligible content items for the request for content 240 b, for example, can depend on content already provided to the same user 202 on the first device 106 a. As a result, an advertisement for California vacations, for example, that is intended for one impression per user can be shown on the first device 106 a and not repeated again on the second different device 106 b. In some implementations, it can be beneficial to provide the same advertisement once and only once to each of the user's multiple devices.

Devices 106 a and 106 b are two examples of devices that the user 202 may use. For example, the user 202 may use a third different device 106 c (e.g., a smart phone). When the user 202 uses the third different device 106 c to log in, for example, the user login service 120 can store a third different anonymous identifier 232 in the linked anonymous identifiers 122. As a result, all three devices 106 a-106 c can be associated with the user 202, e.g., using the secret key 230 a.

Similarly, other users can use the user login service 120 for logging in from multiple different devices. As a result of a second user logging into a fourth and a fifth device 106, for example, the user login service 120 can store fourth and fifth different anonymous identifiers in the linked anonymous identifiers 122 (e.g., stored in association with the second user using a secret key 230 that is different from the secret key 230 a).

FIG. 2F shows example calculations of public, private and secret keys. Device A calculations 250 provide examples for computing a public key, a private key and a secret key on a first device, e.g., the first device 106 a. Device B calculations 252 provide examples for computing a public key, a private key and a secret key on a second different device, e.g., the second different device 106 b. Other methods can be used to determine public, private and secret keys.

In some implementations, the calculations can occur in steps, e.g., steps 254 a-254 e. For example, in step 1 254 a, both devices A and B can exchange a prime P (e.g., 11) and a generator G (e.g., 7). In some implementations, the prime and generator can be stored in the user login information 121, as described above. For example, a prime and a generator that is unique to a user (and the devices associated with the user) can be determined and stored at a time that one or more entries in the user login information 121 are created and stored.

In step 2 254 b, each device can generate its own private key, e.g., using a random number or in some other way. For example, device A's private key can be 6, and device B's private key can be 9. These private keys can be used in combination with at least the generator and prime from step 1 254 a to determine public and private keys in the following steps.

In step 3 254 c, each device can compute a public key. In some implementations, computing the public key can use a formula that includes the generator raised to the power of the device's private key, and a modulo P can be performed on the result. Using the generator, prime, and each of the devices' private keys, the resulting public keys for the devices can result in being 4 and 8, respectively.

At step 4 254 d, once the public keys are determined, the devices can share their public keys, e.g., by publishing the keys in the user login information 121 as described above. As a result, device A can know device B's public key (e.g., 8), and device B can know device A's public key (e.g., 4).

At step 5 254 e, secret keys can be computed, e.g., using a formula that raises the other device's public key to power of the current device's private key, and the result can undergo a modulo P (prime). As a result of the calculations, the secret key for the first and second devices can be 3. Once the secret key is determined, the value can be used by either device to update the row in the linked anonymous identifiers 121 with the device's anonymous identifier. This can be repeated for any other device associated with the same user that computes the secret key using its own private key and the public key from one of the other devices.

FIG. 3A is a flowchart of an example process 300 for providing content to a user on any of multiple devices associated with the user. In some implementations, the content management system 110 and/or the user login service 120 can perform steps of the process 300 using instructions that are executed by one or more processors. FIGS. 1-2F are used to provide example structures for performing the steps of the process 300.

A first login request is received from a first device used by a user for logging into a service, the first login request being associated with a first anonymous identifier associated with the first device (302). For example, referring to FIG. 2A, the user login service 120 can receive the login request 208 a from the first device 106 a (e.g., a personal computer) being used by the user 202. The login request can be associated, for example, with the anonymous identifier 206 a (e.g., “Device ID 1”) that is associated with the first device 106 a.

A seed is read, and a first private-public key pair is created that is associated with the user when using the first device (304). As an example, the user login service 120 can read the initial seed number 212 a (e.g., generator-prime pair 7, 11) and provide the initial seed number 212 a to the first device 106 a. Using the seed, the first device 106 a can determine the private key (e.g., 9) and the public key (e.g., 4) associated with first device 106 a.

A first private key associated with the first private-public key pair is stored locally in the first device, and a first public key is published in a directory entry associated with the user (306). The first device 106 a, for example, can store the private key in local storage 221 a. The first device 106 a can also provide the public key (e.g., 4) to the user login service 120 for storage in user login information 121.

A second login request is received from a second different device used by the user, the second login request being associated with a second different anonymous identifier associated with the second different device (308). As an example, referring to FIG. 2B, the same user 202 can log into the second different device (e.g., a laptop computer). The user login service 120, for example, can receive the login request 208 b. The login request can be associated, for example, with the anonymous identifier 206 b (e.g., “Device ID 2”) that is associated with the second different device 106 b.

Responsive to the received second login request (310), the seed is read, and a second private-public key pair is created that is associated with the user when using the second different device including a second different public key (312). As an example, the user login service 120 can read the initial seed number 212 a (e.g., generator-prime pair 7, 11) and provide the initial seed number 212 a to the second different device 106 b. Using the seed, the second different device 106 b can determine its private key (e.g., 6) and the public key (e.g., 8).

A second private key associated with the second private-public key pair is stored locally in the second different device, and the second public key is published in the directory entry associated with the user (314). The second different device 106 b, for example, can store the private key in local storage 221 b. The second different device 106 b can also provide the public key (e.g., 8) to the user login service 120 for storage in user login information 121.

A secret key is created using the first public key (316). For example, referring to FIG. 2C, the second different device 106 b can compute the secret key 230 a (e.g., 3) using the public key (e.g., 4) from the first device and the second different device's own private key (e.g., 6). Device B calculations 502 shown in FIG. 2F provide example steps and formulas for computing the secret key.

The second anonymous identifier is associated with the secret key (318). For example, the second different anonymous identifier (e.g., Device ID 2) can be stored with the secret key (e.g., a hashed version), e.g., in the linked anonymous identifiers 122, which is stored separately from the user login information 121.

At a time subsequent to the publishing of the second public key, a login request is received from the user when accessing the first device (320) and, responsive to the received request, the secret key is created using the second public key (322). As an example, the user 202 can log back into the first device 106 a. The login request 208 a, for example, can be received by the user login service 120. At this time, the first device 106 a can also compute the secret key 3 using the first device's private key (e.g., 9) and the public key (e.g., 8) from the second different device 106 b. Device A calculations 500 shown in FIG. 2F provide example steps and formulas for computing the secret key.

The first anonymous identifier is associated with the secret key (324). For example, the first anonymous identifier (e.g., Device ID 2) can be stored with hashed version of the secret key in the linked anonymous identifiers 122. As a result, both anonymous identifiers are now linked. For example, the secret key, the first anonymous identifier, and the second different anonymous identifier are stored as an entry in a table, e.g., row 234. In some implementations, the association maps the secret key to both the first and the second different anonymous identifiers. In some implementations, one or more associations can be removed (e.g., deleted from the linked anonymous identifiers 122) after expiration of a first time period (e.g., 24 hours, 48 hours, or some other time period). In some implementations, the time period can be associated with an amount of time after which the user would have been expected to have logged out from either the first device or the second different device.

A request for content is received from either the first device including the first anonymous identifier or the second different device including the second different anonymous identifier (326). In one example, referring to FIG. 2E, the content management system 110 can receive, from the first device 106 a, the request for content 240 a that includes the anonymous identifier Device ID 1. In another example, the content management system 110 can receive, from the second different device 106 b, the request for content 240 b that includes the anonymous identifier Device ID 2.

Content is provided in response to the request using the association (328). For example, depending on which device sent the request for content 240 a or 240 b, the content management system 110 can provide content items 246 a or 246 b to either the first device 106 a or the second different device 106 b, respectively.

In some implementations, providing content in response to the request can further include identifying the user based on the association and providing content of interest to the user. For example, information (e.g., an interest in sports) that the user has provided in a user profile (or other information provided by and/or known about the user) can be used to select content which is likely of interest to the user.

Some implementations of the process 300 can include steps for linking additional devices, e.g., a third device and/or additional devices. For example, a login request can be received from a third different device used by the user, the login request being associated with a third different anonymous identifier associated with the third different device. A third different public-private key pair can be created, including a third public key. The third private key can be stored locally on the third different device, and the third public key can be published (e.g., in the user login information 121). A secret key can be created using one of either the first public key or the second public key, in addition to the third different device's private key, e.g., using steps and formulas shown in FIG. 2F. An association between the secret key, the first anonymous identifier, the second different anonymous identifier and the third different anonymous identifier can be stored, e.g., in the linked anonymous identifiers 122. Subsequently, a request for content can be received from either the first device including the first anonymous identifier, the second different device including the second different anonymous identifier, or the third different device including the third different anonymous identifier. In response to request, content (e.g., content items 246 a or 246 b, or content items for the third different device) can be provided using the association.

FIG. 3B is a flowchart of an example process 340 for providing content to a user on any of multiple linked devices associated with the user. In some implementations, the content management system 110 and/or the user login service 120 can perform steps of the process 340 using instructions that are executed by one or more processors. FIGS. 1-2F are used to provide example structures for performing the steps of the process 340.

Multiple anonymous identifiers associated with a user are linked by a service using a key exchange protocol without storing personally identifiable information associated with the user in the linking (342). For example, anonymous identifiers (e.g., browser cookies, or device Device IDs 1 and 2) of the first device 106 a and the second different device 106 b, respectively, can be linked by the user login service 120. The linking, for example, can occur using key exchange techniques described above, including using public, private and secret key calculations shown in FIG. 2E. In some implementations, public keys can be published on the user login service 120, private keys can be stored on the corresponding local device, and secret keys can be stored in a third location (e.g., linked anonymous identifiers 122). Other techniques can be used to link the devices, and more than two devices can be linked.

In some implementations, linking multiple anonymous identifiers can include receiving a login request (e.g., login requests 208 a or 208 b) from the user from plural different devices, determining a secret key using published public key information from another device associated with the user (where the secret key does not include any personally identifiable information associated with the user) and mapping the secret key to an anonymous identifier associated with each login request. For example, the secret key can be a secret key stored in the linked anonymous identifiers 122, which does not include information about the user that can be traced back to the user (i.e., without having access to the information from the user login information 121, the linked anonymous identifiers 122, and private keys stored on the various user devices).

In some implementations, determining the secret key can include, at each device, creating a public-private key pair, publishing a public key of the public-private key pair, and using a private key of the public-private key pair and a public key of another device to compute the secret key.

Requests for content from a client device associated with the user are received at the service, where each request includes one of the anonymous identifiers (344). For example, referring to FIG. 2E, the content management system 110 can receive the request for content 240 a that includes the anonymous identifier Device ID 1 corresponding to the first device 106 a. In another example, the content management system 110 can receive the request for content 240 b that includes the anonymous identifier Device ID 2 corresponding to the second different device 106 b.

Content associated with the user is provided that is responsive to the received requests and based on the linking (346). For example, the content management system 110 can provide content items 246 a or 246 b to either the first device 106 a or the second different device 106 b, respectively, depending on which device sent the request for content 240 a or 240 b.

FIG. 3C is a flowchart of an example process 360 for providing content to a user on any of multiple devices linked using public-private keys. In some implementations, the content management system 110 and/or the user login service 120 can perform steps of the process 360 using instructions that are executed by one or more processors. FIGS. 1-2F are used to provide example structures for performing the steps of the process 360.

Public-private key pairs are created for a user each time the user logs into a service from a different device including publishing respective public keys of the user in a directory entry associated with the user (362). For example, FIGS. 2A-2D show a sequence of actions that use public-private key pairs to link the first device 106 a and the second different device 106 b. The public keys in this example are stored in the user login information 121.

A secret key is created by each device using a public key of another device that is stored in the directory (364). For example, FIGS. 2C-2D show a sequence of actions that determine the secret key for each of the first device 106 a and the second different device 106 b using the public key of the other device.

The secret keys are associated with a plurality of anonymous identifiers, each anonymous identifier assigned to the user during a session associated with a respective different device (366). As an example, the secret key is stored in the linked anonymous identifiers 122. Steps and formulas for computing the secret keys are shown in FIG. 2E.

Content is provided that is associated with the user and based at least in part on the association (368). For example, depending on which device sent the request for content 240 a or 240 b, the content management system 110 can provide content items 246 a or 246 b to either the first device 106 a or the second different device 106 b, respectively.

FIG. 4 is a block diagram of computing devices 400, 450 that may be used to implement the systems and methods described in this document, as either a client or as a server or plurality of servers. Computing device 400 is intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. Computing device 400 is further intended to represent any other typically non-mobile devices, such as televisions or other electronic devices with one or more processers embedded therein or attached thereto. Computing device 450 is intended to represent various forms of mobile devices, such as personal digital assistants, cellular telephones, smartphones, and other computing devices. The components shown here, their connections and relationships, and their functions, are meant to be exemplary only, and are not meant to limit implementations of the inventions described and/or claimed in this document.

Computing device 400 includes a processor 402, memory 404, a storage device 406, a high-speed interface 408 connecting to memory 404 and high-speed expansion ports 410, and a low speed interface 412 connecting to low speed bus 414 and storage device 406. Each of the components 402, 404, 406, 408, 410, and 412, are interconnected using various busses, and may be mounted on a common motherboard or in other manners as appropriate. The processor 402 can process instructions for execution within the computing device 400, including instructions stored in the memory 404 or on the storage device 406 to display graphical information for a GUI on an external input/output device, such as display 416 coupled to high speed interface 408. In other implementations, multiple processors and/or multiple buses may be used, as appropriate, along with multiple memories and types of memory. Also, multiple computing devices 400 may be connected, with each device providing portions of the necessary operations (e.g., as a server bank, a group of blade servers, or a multi-processor system).

The memory 404 stores information within the computing device 400. In one implementation, the memory 404 is a computer-readable medium. In one implementation, the memory 404 is a volatile memory unit or units. In another implementation, the memory 404 is a non-volatile memory unit or units.

The storage device 406 is capable of providing mass storage for the computing device 400. In one implementation, the storage device 406 is a computer-readable medium. In various different implementations, the storage device 406 may be a floppy disk device, a hard disk device, an optical disk device, or a tape device, a flash memory or other similar solid state memory device, or an array of devices, including devices in a storage area network or other configurations. In one implementation, a computer program product is tangibly embodied in an information carrier. The computer program product contains instructions that, when executed, perform one or more methods, such as those described above. The information carrier is a computer- or machine-readable medium, such as the memory 404, the storage device 406, or memory on processor 402.

The high speed controller 408 manages bandwidth-intensive operations for the computing device 400, while the low speed controller 412 manages lower bandwidth-intensive operations. Such allocation of duties is exemplary only. In one implementation, the high-speed controller 408 is coupled to memory 404, display 416 (e.g., through a graphics processor or accelerator), and to high-speed expansion ports 410, which may accept various expansion cards (not shown). In the implementation, low-speed controller 412 is coupled to storage device 406 and low-speed expansion port 414. The low-speed expansion port, which may include various communication ports (e.g., USB, Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or more input/output devices, such as a keyboard, a pointing device, a scanner, or a networking device such as a switch or router, e.g., through a network adapter.

The computing device 400 may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a standard server 420, or multiple times in a group of such servers. It may also be implemented as part of a rack server system 424. In addition, it may be implemented in a personal computer such as a laptop computer 422. Alternatively, components from computing device 400 may be combined with other components in a mobile device (not shown), such as device 450. Each of such devices may contain one or more of computing device 400, 450, and an entire system may be made up of multiple computing devices 400, 450 communicating with each other.

Computing device 450 includes a processor 452, memory 464, an input/output device such as a display 454, a communication interface 466, and a transceiver 468, among other components. The device 450 may also be provided with a storage device, such as a microdrive or other device, to provide additional storage. Each of the components 450, 452, 464, 454, 466, and 468, are interconnected using various buses, and several of the components may be mounted on a common motherboard or in other manners as appropriate.

The processor 452 can process instructions for execution within the computing device 450, including instructions stored in the memory 464. The processor may also include separate analog and digital processors. The processor may provide, for example, for coordination of the other components of the device 450, such as control of user interfaces, applications run by device 450, and wireless communication by device 450.

Processor 452 may communicate with a user through control interface 458 and display interface 456 coupled to a display 454. The display 454 may be, for example, a TFT LCD display or an OLED display, or other appropriate display technology. The display interface 456 may comprise appropriate circuitry for driving the display 454 to present graphical and other information to a user. The control interface 458 may receive commands from a user and convert them for submission to the processor 452. In addition, an external interface 462 may be provided in communication with processor 452, so as to enable near area communication of device 450 with other devices. External interface 462 may provide, for example, for wired communication (e.g., via a docking procedure) or for wireless communication (e.g., via Bluetooth or other such technologies).

The memory 464 stores information within the computing device 450. In one implementation, the memory 464 is a computer-readable medium. In one implementation, the memory 464 is a volatile memory unit or units. In another implementation, the memory 464 is a non-volatile memory unit or units. Expansion memory 474 may also be provided and connected to device 450 through expansion interface 472, which may include, for example, a subscriber identification module (SIM) card interface. Such expansion memory 474 may provide extra storage space for device 450, or may also store applications or other information for device 450. Specifically, expansion memory 474 may include instructions to carry out or supplement the processes described above, and may include secure information also. Thus, for example, expansion memory 474 may be provide as a security module for device 450, and may be programmed with instructions that permit secure use of device 450. In addition, secure applications may be provided via the SIM cards, along with additional information, such as placing identifying information on the SIM card in a non-hackable manner.

The memory may include for example, flash memory and/or MRAM memory, as discussed below. In one implementation, a computer program product is tangibly embodied in an information carrier. The computer program product contains instructions that, when executed, perform one or more methods, such as those described above. The information carrier is a computer- or machine-readable medium, such as the memory 464, expansion memory 474, or memory on processor 452.

Device 450 may communicate wirelessly through communication interface 466, which may include digital signal processing circuitry where necessary. Communication interface 466 may provide for communications under various modes or protocols, such as GSM voice calls, SMS, EMS, or MMS messaging, CDMA, TDMA, PDC, WCDMA, CDMA2000, or GPRS, among others. Such communication may occur, for example, through radio-frequency transceiver 468. In addition, short-range communication may occur, such as using a Bluetooth, WiFi, or other such transceiver (not shown). In addition, GPS receiver module 470 may provide additional wireless data to device 450, which may be used as appropriate by applications running on device 450.

Device 450 may also communicate audibly using audio codec 460, which may receive spoken information from a user and convert it to usable digital information. Audio codec 460 may likewise generate audible sound for a user, such as through a speaker, e.g., in a handset of device 450. Such sound may include sound from voice telephone calls, may include recorded sound (e.g., voice messages, music files, etc.) and may also include sound generated by applications operating on device 450.

The computing device 450 may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a cellular telephone 480. It may also be implemented as part of a smartphone 482, personal digital assistant, or other mobile device.

Various implementations of the systems and techniques described here can be realized in digital electronic circuitry, integrated circuitry, specially designed ASICs (application specific integrated circuits), computer hardware, firmware, software, and/or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

These computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. As used herein, the terms “machine-readable medium” “computer-readable medium” refers to any computer program product, apparatus and/or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term “machine-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor.

To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), and the Internet.

The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous. 

What is claimed is:
 1. A computer-implemented method comprising: receiving a first login request from a first device used by a user for logging into a service, the first login request being associated with a first anonymous identifier associated with the first device; reading a seed and creating, using one or more processors, a first private-public key pair associated with the user when using the first device; storing a first private key associated with the first private-public key pair locally in the first device and publishing a first public key in a directory entry associated with the user; receiving a second login request from a second different device used by the user, the second login request being associated with a second different anonymous identifier associated with the second different device; responsive to the received second login request: reading the seed and creating a second private-public key pair associated with the user when using the second different device including a second different public key; storing a second private key associated with the second private-public key pair locally in the second different device and publishing the second public key in the directory entry associated with the user; creating a secret key using the first public key; and associating the second anonymous identifier with the secret key; at a time subsequent to the publishing of the second public key, receiving a login request from the user when accessing the first device and, responsive to the received request: creating the secret key using the second public key; and associating the first anonymous identifier with the secret key; receiving a request for content from either: the first device including the first anonymous identifier; or the second different device including the second different anonymous identifier; and providing, using the one or more processors, content in response to the request using the association.
 2. The method of claim 1 wherein the directory entry is stored in a directory that includes one or more entries, each entry indexed by an identifier associated with a given user.
 3. The method of claim 2 wherein the identifier is a user login identifier.
 4. The method of claim 2 wherein the identifier is an email address associated with the user.
 5. The method of claim 1 wherein the first and second different anonymous identifiers are associated with different browsers.
 6. The method of claim 1 wherein receiving the login request includes receiving a request to log into a social service.
 7. The method of claim 1 further comprising storing an association between the secret key and the first and second anonymous identifiers including storing the secret key, the first anonymous identifier, and the second different anonymous identifier as an entry in a table.
 8. The method of claim 7 wherein storing the association includes mapping the secret key to both the first and the second different anonymous identifiers.
 9. The method of claim 7 wherein storing the association includes removing the association after expiration of a first time period.
 10. The method of claim 9 wherein the first time period is associated with an amount of time after which the user would have been expected to have logged out from either the first device or the second different device.
 11. The method of claim 1 wherein the first and second different anonymous identifiers are selected from the group comprising a browser cookie or a device identifier.
 12. The method of claim 1 further comprising: receiving a login request from a third different device used by the user, the login request being associated with a third different anonymous identifier associated with the third different device; creating a third different public-private key pair including a third public key; storing the third private key locally on the third different device and publishing the third public key; creating the secret key using one of either the first public key or the second public key; storing an association between the secret key, the first anonymous identifier, the second different anonymous identifier and the third different anonymous identifier; receiving a request for content from either: the first device including the first anonymous identifier; the second different device including the second different anonymous identifier; or the third different device including the third different anonymous identifier; and providing content in response to the request and using the association.
 13. The method of claim 1 wherein receiving a request for content includes receiving a request for advertising content.
 14. The method of claim 1 wherein receiving a request for content includes receiving a request from the first device including the first anonymous identifier, wherein the first anonymous identifier is a cookie.
 15. The method of claim 1 wherein providing content in response to the request further includes identifying the user based on the association and providing content of interest to the user.
 16. A computer-implemented method comprising: linking, using one or more processors, multiple anonymous identifiers associated with a user by a service using a key exchange protocol without storing personally identifiable information associated with the user in the linking; receiving, at the service, requests for content from a client device associated with the user, wherein each request includes one of the anonymous identifiers; and providing, using the one or more processors, content associated with the user, responsive to the received requests and based on the linking.
 17. The method of claim 16 wherein linking multiple anonymous identifiers includes: receiving a login request from the user from plural different devices; determining a secret key using published public key information from another device associated with the user, wherein the secret key does not include any personally identifiable information associated with the user; and mapping the secret key to an anonymous identifier associated with each login request.
 18. The method of claim 17 wherein the multiple anonymous identifiers are selected from the group comprising browser cookies and device identifiers.
 19. The method of claim 18 wherein determining the secret key includes, at each device: creating a public-private key pair; publishing a public key of the public-private key pair; and using a private key of the public-private key pair and a public key of another device to compute the secret key.
 20. A computer-implemented method comprising: creating, using one or more processors, public-private key pairs for a user each time the user logs into a service from a different device including publishing respective public keys of the user in a directory entry associated with the user; creating, by each device, a secret key using a public key of another device that is stored in the directory that does not include personally identifiable information associated with users; associating the secret keys with a plurality of anonymous identifiers, each anonymous identifier assigned to the user when logged into a respective different device; and providing, using the one or more processors, content associated with the user and based at least in part on the association. 